Alkane Dehydrogenation Catalyst and Methods of Converting Alkanes to Alkenes

ABSTRACT

Provided herein is an alkane dehydrogenation catalyst, a method of manufacturing an alkane dehydrogenation catalyst, and a method of converting alkanes to alkenes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a Divisional of U.S. Non-Provisional patentapplication Ser. No. 17/197,997 filed on Mar. 10, 2021, which claimspriority to U.S. Provisional Patent Application No. 62/987,841 filedMar. 10, 2020; the entire disclosures of which are incorporated hereinby reference.

STATEMENT OF GOVERNMENT SUPPORT

This invention was made with under CRADA No. A18085 between HoneywellUOP and UChicago Argonne, LLC, operator of Argonne National Laboratoryunder Contract No. DE-AC02-06CH11357 awarded by the United StatesDepartment of Energy. The government has certain rights in theinvention.

BACKGROUND

Light alkenes and propylene, in particular, are regarded as criticalbuilding blocks for chemical feed stocks. Propylene is one of the mostcrucial chemical building block in the industry for the production ofchemicals such as polypropylene, acrylonitrile, acrylic acid, andpropylene oxide (Hocking et al., Handbook of chemical technology andpollution control. 2nd ed.; Academic Press: San Diego, 1998; p xxiv, 777p). Due to the significant need for products derived from propylene, thecurrent global propylene demand is approximately 90 million metric tons(MMT), and is expected to increase to 130 MMT by 2023 (Sattler et al.,Chemical Reviews 2014, 114 (20), 10613-10653). Currently, propylene isproduced mainly through steam and 91Zfluidized catalytic cracking ofnaphtha, light diesel, and other oil byproducts. However, these twocommercial approaches cannot meet future demands for propylene.Recently, increases in shale gas production have resulted in a downwardtrend in the price of the propane and therefore increased interest inpropane dehydrogenation (PDH) as a source of propylene. Among themultiple metals known to catalyze dehydrogenation where catalysts havebeen industrially commercialized, platinum based catalysts are among themost successful. (Vora, Top Catal 2012, 55 (19-20), 1297-1308). Platinumbased catalysts/processes are both highly active and very selective tothe desired product. However, under the high reaction temperature (>600°C.), sintering of platinum nanoparticles can occur, which lowers theavailable surface area of the platinum used to catalyze the reaction.With increased sintering, the activity and selectivity to propylenedecreases significantly. A technique developed in the field tocounteract these effects is frequent regeneration under chlorineatmosphere to re-disperse the platinum nanoparticles.

In addition to propane dehydrogenation (PDH), sintering of supportedmetal nanoparticles is a major technical issue limiting the lifetime andperformance of many commercial heterogeneous catalysts. Consequently, inthe field of heterogeneous catalysis there is a tremendous incentive tomitigate sintering and improve catalyst longevity. Most studies in theliterature have focused on powders, but for industrial applications,formed bodies such as extrudates are generally utilized. One strategyfor synthesizing sinter resistant catalysts employs overcoating aprotecting layer to inhibit nanoparticle mobility. However, conventionalovercoatings tend to reduce catalytic activity.

SUMMARY

There is a need for improvements to overcoating nanoparticles tomitigate sintering and improve catalyst longevity, particularly at hightemperatures, without reducing catalytic activity.

In embodiments, a method of manufacturing an alkane dehydrogenationcatalyst comprising a catalyst support, catalytic nanoparticles, and anovercoat, can include: calcining the catalyst support at a temperaturein a range of about 500° C. to about 1200° C., wherein after calcining,the calcined catalyst support has a total surface area of 50 m²/g to 350m²/g; and immersing the calcined catalyst support in a nanoparticleprecursor solution comprising a nanoparticle precursor, under conditionssufficient to impregnate the calcined catalyst support with thenanoparticle precursor and form an impregnated catalyst precursor;calcining the impregnated catalyst precursor under conditions sufficientto convert the nanoparticle precursor impregnated in the impregnatedcatalyst precursor to catalytic nanoparticles to form a calcinedimpregnated catalyst precursor, wherein the calcining is done at atemperature in a range of about 150° C. to about 600° C.; depositing byatomic layer deposition (ALD) the overcoat onto the calcined catalystprecursor by contacting the calcined catalyst precursor with an ALDprecursor and water at a temperature in a range of about 150° C. toabout 300° C., and repeating the depositing step one or more times,thereby forming a catalyst intermediate; annealing the catalystintermediate in air at a temperature of less than about 600° C. forabout 30 minutes to about 2 hours, thereby forming the alkanedehydrogenation catalyst.

In embodiments, an alkane dehydrogenation catalyst, can include: acatalyst support infiltrated with a plurality of catalyticnanoparticles, and; an atomic layer deposition overcoat; wherein theplurality of catalytic nanoparticles have an average size of about 0.6nm to about 1.2 nm, the atomic layer deposition overcoat has a thicknessof about 0.12 nm to about 1.2 nm, the catalyst support has a totalsurface area of 90 m²/g to 300 m²/g, a pore volume of 0.8 cm³/g to 0.4cm³/g, and an average pore size of 6 nm to 17 nm.

In embodiments, a method of converting an alkane to an alkene, caninclude: flowing the gaseous reactant mixture over the alkanedehydrogenation catalyst, according to the disclosure, at a temperaturein a range of about 400° C. to about 800° C. wherein the gaseousreactant mixture comprises hydrogen gas and an alkane gas, and thealkane gas is converted to an alkene as the gaseous reactant mixture isflowed over the alkane dehydrogenation catalyst.

In embodiments, an ALD coated alkane dehydrogenation catalyst, caninclude: a catalyst support infiltrated with a plurality of catalyticnanoparticles to form an alkane dehydrogenation catalyst, wherein thecatalytic nanoparticles comprise at least one metal selected from group8 metals, and the catalyst support is an extrudate, and an atomic layerdeposition overcoat arranged in contact with a portion of a surface ofthe catalytic nanoparticles to form the ALD coated alkanedehydrogenation catalyst, wherein the coated alkane dehydrogenationcatalysis has a hydrogen chemisorption capacity that is substantiallythe same as a hydrogen chemisorption capacity of the uncoated alkanedehydrogenation catalyst.

In embodiments, an ALD coated alkane dehydrogenation catalyst, caninclude: a catalyst support infiltrated with a plurality of catalyticnanoparticles to form an alkane dehydrogenation catalyst, wherein thecatalytic nanoparticles comprise at least one metal selected from group8 metals, and the catalyst support is an extrudate; and an atomic layerdeposition overcoat, wherein the atomic layer deposition overcoat isdeposited onto the alkane dehydrogenation catalyst by 2-5 cycles ofatomic layer deposition when the alkane dehydrogenation catalyst has asurface area of about 80 m²/g to about 100 m²/g or 5-8 cycles of atomiclayer deposition when the alkane dehydrogenation catalyst has a surfacearea of about 80 m²/g to about 100 m²/g.

In embodiments, an ALD coated alkane dehydrogenation catalyst, caninclude: a catalyst support infiltrated with a plurality of catalyticnanoparticles to form an alkane dehydrogenation catalyst, wherein thecatalytic nanoparticles comprise at least one metal selected from group8 metals, and the catalyst support is an alumina extrudate; and anatomic layer deposition overcoat; wherein the alumina extrudate is in aγ phase, a θ phase, a α phase, or a combination thereof.

BRIEF DESCRIPTION OF FIGURES

FIG. 1A is a STEM image of an alkane dehydrogenation catalyst (0.1Pt/ultra-low surface area (SA)) in accordance with embodiments of thedisclosure. The inset shows the Pt nanoparticle size distribution;

FIG. 1B is a STEM image of an alkane dehydrogenation catalyst (0.5Pt/ultra-high SA) in accordance with embodiments of the disclosure. Theinset shows the Pt nanoparticle size distribution;

FIG. 10 is a STEM image of an alkane dehydrogenation catalyst (0.5Pt/medium SA) in accordance with embodiments of the disclosure. Theinset shows the Pt nanoparticle size distribution;

FIG. 1D is a STEM image of an alkane dehydrogenation catalyst (0.5Pt/ultra-low SA) in accordance with embodiments of the disclosure. Theinset shows the Pt nanoparticle size distribution;

FIG. 2 includes dark field STEM images and corresponding EDS maps fromfour different parts of the alkane dehydrogenation catalyst (medium SAAl₂O₃ extrudates after 5 cycles of TiO₂ ALD) in accordance withembodiments of the disclosure;

FIGS. 3A-3H are graphs showing the total surface area and the porevolume for alkane dehydrogenation catalyst in accordance withembodiments of the disclosure. The graphs show the total surface for0.1% and 0.5% Pt catalyst loading on (A) ultra-high SA, (C) high SA, (E)medium SA, and (G) low SA supports. The graphs show the pore volume for0.1% and 0.5% Pt catalyst loading on (B) ultra-high SA, (D) high SA, (F)medium SA, and (H) low SA supports;

FIGS. 4A-4F are graphs showing the H₂ chemisorption results for theAl₂O₃ ALD overcoated catalysts in accordance with embodiments of thedisclosure. The graphs are of the following catalysts: (A) 0.1% Pt and(B) 0.5% Pt, on ultra-high SA (squares), high SA (triangles), medium SA(diamonds), and low SA (circles) supports; (C) 0.5% Pt/ultra-high SA,(D) 0.5% Pt/high SA, (E) 0.5% Pt/medium SA, and (F) 0.5% Pt/low SAcatalysts, samples after Al₂O₃ ALD overcoating (triangles); samplesafter air annealing (circles); samples after 1 h steam treatment(diamonds); samples after 4 h steam treatment (squares);

FIGS. 5A and 5B are graphs showing the C₃H₈ conversion versus C₃H₆selectivity for non-ALD overcoated (A) 0.1% Pt and (B) 0.5% Ptcatalysts. (Data was collected for 20 h with interval of 20 mins; tonormalize the Pt loading for testing, the amount of 0.1% Pt catalystsloaded is 5 times more than the 0.5% Pt catalysts);

FIGS. 6A-6D are graphs showing C₃H₈ conversion versus Al₂O₃ ALD cyclesat the 10^(th) hour for 0.1% Pt catalysts on supports with (A)ultra-high SA, (B) high SA, (C) medium SA, and (D) low SA (gray bar:C₃H₈ conversion and C₃H₆ yield for steamed catalysts; hashed bar: changein C₃H₈ conversion and C₃H₆ yield between fresh and steamed catalysts; 0cycle represents the catalysts without ALD overcoating);

FIGS. 6E-6H are graphs showing C₃H₆ yield versus Al₂O₃ ALD cycles at10^(th) hour for 0.1% Pt catalysts on supports with (E) ultra-high SA,(F) high SA, (G) medium SA, and (H) low SA;

FIGS. 6I-6L are graphs showing C₃H₈ conversion versus Al₂O₃ ALD cyclesat the 10^(th) hour for 0.5% Pt catalysts on supports with (I)ultra-high SA, (J) high SA, (K) medium SA, and (L) low SA (gray bar:C₃H₈ conversion and C₃H₆ yield for steamed catalysts; hashed bar: changein C₃H₈ conversion and C₃H₆ yield between fresh and steamed catalysts; 0cycle represents the catalysts without ALD overcoating);

FIGS. 6M-6P are graphs showing C₃H₆ yield versus Al₂O₃ ALD cycles at the10^(th) hour for 0.5% Pt catalysts on supports with (M) ultra-high SA,(N) high SA, (O) medium SA, and (P) low SA (gray bar: C₃H₈ conversionand C₃H₆ yield for steamed catalysts; hashed bar: change in C₃H₈conversion and C₃H₆ yield between fresh and steamed catalysts; 0 cyclerepresents the catalysts without ALD overcoating);

FIG. 7 is a graph of the turnover frequency (TOF) of C₃H₆ at the 10^(th)hour during the reaction for 0.5% Pt loaded catalysts versus Al₂O₃ ALDcycle, comparing catalyst supports having ultra-high, high, and mediumsurface areas;

FIGS. 8A-8D are graphs of the products selectivity for fresh 0.1% Ptcatalysts on supports with (A) ultra-high SA, (B) high SA, (C) mediumSA, and (D) low SA;

FIGS. 8E-8H are graphs of the products selectivity for fresh 0.5% Ptcatalysts on supports with (E) ultra-high SA, (F) high SA, (G) mediumSA, and (H) low SA; and

FIG. 9 shows a picture of two different ALD systems for use in methodsof the disclosure. The picture on the right shows a pilot scale highthroughput semi-continuous ALD system designed for 4 ALD cycles at up to15 kg/h rates. The picture on the left shows a single cycle towerton-scale semi-continuous ALD system for 240 kg/h rates. The schematicin the middle indicates the sequential steps of the ALD process for eachsystem.

DETAILED DESCRIPTION

In accordance with embodiments, alkane dehydrogenation catalysts caninclude a catalyst support infiltrated with a plurality of catalyticnanoparticles and an atomic layer deposition (ALD) overcoat. It has beenadvantageously found that the alkane dehydrogenation catalysts of thedisclosure have improved resistance to sintering, while maintaining goodcatalytic activity and selectivity towards alkenes. Without intending tobe bound by theory, it is believed that the improved performance is, atleast in part, due to the presence of a thin ALD overcoat applied to thecatalytic nanoparticle and catalyst support. Further, advantageouslycatalyst in accordance with embodiments of the disclosure can be formedusing extrudates as catalysts supports, which can be advantageous overconventional powders.

In embodiments, the alkane dehydrogenation catalyst provided herein canmaintain catalytic activity and selectivity towards alkenes after a 1hour steam treatment at 700° C. In embodiments, the alkanedehydrogenation catalyst provided herein can maintain catalytic activityand selectivity towards alkenes after a 4 hour steam treatment at 700°C. In embodiments, the alkane dehydrogenation catalyst provided hereincan maintain catalytic activity and selectivity towards alkenes after 2or more 1 hour steam treatments at 700° C. In embodiments, the alkanedehydrogenation catalyst provided herein can maintain catalytic activityand selectivity towards alkenes after 5 or more 1 hour steam treatmentsat 700° C. In embodiments, the alkane dehydrogenation catalyst providedherein can maintain catalytic activity and selectivity towards alkenesafter 2 or more 4 hour steam treatments at 700° C. In embodiments, thealkane dehydrogenation catalyst provided herein can maintain catalyticactivity and selectivity towards alkenes after 400 or more 4 hour steamtreatments at 700° C.

Generally, catalysts having good catalytic activity and/or maintainedcatalytic activity have an alkane conversion in a range of about 5% toabout thermodynamic equilibrium level of alkane conversion. For example,the catalysts of the disclosure can have a catalytic activity beforeand/or after heat treatments of about 5% to about 50%, or about 5% toabout 40%, or about 5% to about 30%.

Generally, catalysts of the disclosure can have and/or maintain, afterthermal treatment, an alkene selectivity of about 70% or more, such asabout 80% or more, or about 85% or more, or about 90% or more.

Without intending to be bound by theory, it is believed that reductionin catalytic activity of conventional Pt alkane dehydrogenationcatalysts was due to sintering of small Pt nanoparticles into large Ptclusters, thereby decreasing the metallic surface area available forreaction.

Catalysts of the disclosure advantageously having an atomic layerdeposited overcoat that preferentially deposits on non-catalyticnanoparticle sites, thus providing protection against sintering withoutreducing the catalytic activity of the active catalytic nanoparticlesites.

As used herein, the term “non-active catalytic nanoparticle sites”refers to nanoparticle sites that have no or substantially no adsorbedH₂ when subject to the Chemisorption Test method described in detailbelow. For example, less than 5%, less than 1%, less than 0.5%, of thetotal adsorbed H₂ as measured by the Chemisorption Test Method can beadsorbed by the non-active catalytic nanoparticle sites.

In accordance with embodiments, a method of manufacturing an alkanedehydrogenation catalyst is provided. In embodiments, the method ofmanufacturing a coated alkane dehydrogenation catalyst can includeperforming a hydrogen chemisorption test described herein as theChemisorption Test Method, at interim stages of the coating and/or atthe end of the coating to determine the percent catalytically activesites remaining after coating. This can be useful in determining whetheradditional coating can be applied, such as through additional ALD cyclesas described herein. In embodiments, the coating can be applied untilthe percent of active sites is about 50% as measured by theChemisorption Test Method. Other suitable threshold percentages for theamount of active sites are also contemplated herein.

In accordance with embodiments, a method of converting alkanes toalkenes is provided. The method can include an alkane dehydrogenationcatalyst and a gaseous reactant. The gaseous reactant mixture caninclude an alkane. The method of converting alkanes to alkenes canadvantageously have an equilibrium conversion of alkanes to alkenesbetween about 30% to about 40%, a total amount of thermal cracking ofthe catalyst of less than 3% after 20 hours (e.g., less than 1% ),and/or an alkene selectivity of greater than about 85%.

Alkane Dehydrogenation Catalyst

The alkane dehydrogenation catalyst can include a catalyst supportinfiltrated with a plurality of catalytic nanoparticles and an atomiclayer deposition overcoat. In embodiments, the plurality of catalyticnanoparticles have an average size of about 0.6 nm to about 1.2 nm. Inembodiments, the atomic layer deposition overcoat has a thickness ofabout 1.2 Å to about 1.2 nm. In embodiments, the catalyst support has atotal surface area of 50 m²/g to 300 m²/g. In embodiments, the catalystsupport has a pore volume of 0.8 cm³/g to 0.4 cm³/g. In embodiments, thecatalyst support has an average pore size of 6 nm to 17 nm. Inembodiments, the plurality of catalytic nanoparticles have an averagesize of about 0.6 nm to about 1.2 nm, the atomic layer depositionovercoat has a thickness of about 0.12 nm to about 1.2 nm, the catalystsupport has a total surface area of 50 m²/g to 300 m²/g, a pore volumeof 0.8 cm³/g to 0.4 cm³/g, and an average pore size of 6 nm to 17 nm.

In any of the embodiments herein, the catalyst support can be anextrudate or other formed bodies known in the art. The extrudatesdisclosed herein can be porous. In embodiments, the extrudate caninclude a ceramic and/or metal oxide material, such as alumina. Inembodiments, the ceramic and/or metal oxide material can be in one ormore different polymorph phases. For example, when the extrudate isalumina, the alumina can be in a γ phase, a θ phase, an a phase, or acombination thereof. In embodiments, each extrudate polymorph phase,independently, has a different surface area corresponding to it. Forexample, a θ/α a phase of an alumina extrudate can have a surface areaof about 80 m²/g to about 100 m²/g, while a γ/θ phase of an aluminaextrudate can have a surface area of about 200 m²/g to about 220 m²/g.In embodiments wherein the extrudate is alumina, the alumina extrudatecan be in the θ/α a phase and have a surface area of about 80 m²/g toabout 100 m²/g.

In embodiments, the catalyst support can include one or more of alumina(Al₂O₃). silica, aluminum phosphate, titania, zirconia, and acombination thereof.

The surface areas and porosities disclosed herein can be and, inembodiments, were measured using nitrogen gas (N₂) physisorption byBrunauer-Emmett-Teller (BET) analysis.

The catalyst support can have a total surface area of about 10 m²/g ormore. In embodiments, the catalyst support can have a total surface areaof about 10 m²/g to about 1000 m²/g, about 10 m²/g to about 500 m²/g,about 50 m²/g to about 300 m²/g, about 60 m²/g to about 250 m²/g, about60 m²/g to about 200 m²/g, or about 70 m²/g to about 150 m²/g, or about80 m²/g to about 100 m²/g. For example, the catalyst support can have atotal surface area of about 50 m²/g, about 60 m²/g, about 70 m²/g, about75 m²/g, about 80 m²/g, about 85 m²/g, about 90 m²/g, about 95 m²/g,about 100 m²/g, about 105 m²/g, about 110 m²/g, about 120 m²/g, about130 m²/g, about 140 m²/g, about 150 m²/g, about 200 m²/g, about 210m²/g, about 250 m²/g, about 280 m²/g, or about 300 m²/g.

In embodiments, maintaining a total surface area of the catalyst supportof about 50 m²/g to about 120 m²/g was found to require a lower amountof ALD overcoat needed to maintain a high level of stability.

The catalyst support can have a pore volume of about 0.1 cm³/g or more.In embodiments, the catalyst support can have a pore volume of about 0.1cm³/g to about 1 cm³/g, or about 0.2 cm³/g to about 0.9 cm³/g, or about0.3 cm³/g to about 0.9 cm³/g, or about 0.4 cm³/g to about 0.8 cm³/g, orabout 0.5 cm³/g to about 0.8 cm³/g. For example, the catalyst supportcan have a pore volume of about 0.1 cm³/g, 0.2 cm³/g, 0.3 cm³/g, 0.4cm³/g, 0.5 cm³/g, 0.6 cm³/g, 0.7 cm³/g, 0.8 cm³/g, 0.9 cm³/g, or 1cm³/g.

The catalyst support can have an average pore size as determined by N₂physisorption measurements of about 1 nm to about 30 nm. In embodiments,the catalyst support can have an average pore sized of about 5 nm toabout 25 nm, about 5 nm to about 20 nm, about 5 nm to about 18 nm, about6 nm to about 17 nm, or about 7 nm to about 16 nm. For example, thecatalyst support can have an average pore size of about 1 nm, 5 nm, 6nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm,17 nm, 20 nm, 25 nm, or 30 nm.

The plurality of catalytic nanoparticles can include and/or be atransition metal. In embodiments, the plurality of catalyticnanoparticles can include and/or be one or more of platinum, palladium,ruthenium, rhodium, or iridium. In embodiments, the plurality ofcatalytic nanoparticles can include platinum, palladium, or acombination thereof. In embodiments, the plurality of catalyticnanoparticles can include platinum. The plurality of catalyticnanoparticles have an average size of about 0.1 nm or more. Inembodiments, the plurality of catalytic nanoparticles have an averagesize of about 0.3 nm to about 2 nm, about 0.5 nm to about 1.8 nm, about0.6 nm to about 1.5 nm, about 0.6 nm to about 1.2 nm, about 0.7 nm toabout 1 nm. For example, the average size of the plurality of catalyticnanoparticles can be about 0.1 nm, 0.2 nm, 0.3 nm, 0.4 nm, 0.5 nm, 0.6nm, 0.7 nm, 0.8 nm, 0.9 nm, 1 nm, 1.1 nm, 1.2 nm, 1.3 nm, 1.5 nm, orabout 2 nm.

Atomic layer deposition (ALD) is a thin film deposition technique basedon sequential self-limiting surface reactions with gas phase precursors.These reactions take place from gas-phase chemical precursors which areindividually and alternately dosed into and removed from a reactor toform no more than monolayer films. In embodiments, the atomic layerdeposition overcoat can be deposited by high throughput atomic layerdeposition.

Conventional catalyst overcoating with ALD systems often result in densecoatings that hampered or reduced the catalytic activity. This resultedfrom the use of conventional ALD coating equipment and processparameters, which were designed for coating dense, planar substratessuch as the silicon wafers used by the microelectronics industry.

By adjusting the deposition conditions, conventional ALD equipment canbe used to coat small quantities of catalyst substrates such as powdersand extrudates, in single-gram batches. Although this process isacceptable for bench-scale research, it is time consuming, wasteful ofprecursor, and impractical to scale for catalyst manufacturing. It hasbeen advantageously found that a high-throughput particle ALD coatingprocess that delivers lean manufacturing approaches can supplanttraditional batch ALD reactor systems, for low-cost adoption. The ALDprocess suitable for use in the methods of the disclosure is furtherdescribed in Example 7 and FIG. 9 , as well as U.S. Pat. Nos. 9,284,643& 9,546,424, which are incorporated herein in their entirety.

Although any sequence is feasible, in embodiments, the ALD reactionsherein can include an A/B/A/B sequence or an A/B/C/A/B/C sequence,wherein A and B are different ALD precursors, and A, B, and C aredifferent ALD precursors. ALD allows for precise thickness control andconformal deposition on highly porous substrates. In embodiments whereinthe ALD reaction includes an A/B sequence, the ALD precursors caninclude for A: Al, Ti, Nb, Zr, and V; and for B: water, hydrogenperoxide or the like. In embodiments, the ALD precursor: A can includetrimethylaluminum, diethyl zinc, titanium tetraisopropoxide, titaniumtetrachloride, or the like.

In embodiments, the calcined catalyst precursors can be loaded into anALD reactor and heated to a temperature in a range of about 200° C. toabout 500° C. (e.g., about 300° C.) for about 1 hour to about 12 hours.In an embodiment, the temperature can be about 300° C., with a heatingtime of about 2 hours. In embodiments, said process can take place undervacuum to remove adventitious moisture from the system. In embodiments,the catalyst precursors loaded in the ALD reactor at a temperature in arange of about 200° C. to about 500° C. can be cooled to a lowertemperature, for example, about 300° C. to about 200° C.). Inembodiments, an inert gas (for example, N₂) can be flowed through thereactor for the duration of the experiment to act as a carrier gas forthe reaction. In embodiments, the ALD reaction can include an A/Bsequence, such as trimethylaluminum and water as the ALD precursors. Inembodiments, wherein trimethylaluminum and water are used as ALDprecursors, an aluminum oxide film can be formed with methane forming asthe reaction by-product. Different numbers of ALD precursor (e.g., TMAand water) “cycles”, the process of dosing each ALD precursor once toform a monolayer film, can be completed to form the ALD overcoat (e.g.,aluminum oxide layers) of varying thickness on the calcined catalystprecursor. The reactor can then be cooled to room temperature and thecoated catalyst (catalyst intermediate) can be unloaded. The catalystintermediate can then be stored in dry boxes to limit moisture uptakeduring storage.

The atomic layer deposition overcoat can include one or more of Al, Ti,Nb, Zr, and V. In embodiments, the atomic layer deposition overcoat caninclude one or more of Al₂O₃, TiO₂, ZrO₂, Nb₂O₅, and V₂O₅. Inembodiments, the atomic layer deposition overcoat can include one ormore of Al₂O₃, TiO₂, and ZrO₂. In embodiments, the atomic layerdeposition overcoat can comprise Al₂O₃.

The atomic layer deposition overcoat can have a thickness of about 1 Åor more. In embodiments, the atomic layer deposition overcoat can have athickness of about 1 Å to about 10 nm, or about 1 Å to about 5 nm, orabout 1 Å to about 2 nm, or about 1 Å to about 1.2 nm, or about 1.2 Å toabout 1 nm, or 1.2 Å to about 0.8 nm, or about 5 Å to about 1.2 nm orabout 5 Å to about 1.1 nm. For example, the atomic layer depositionovercoat can have a thickness of about 1 Å, 1.1 Å, 1.2 Å, 1.3 Å, 1.5 Å,2 Å, 3 Å, 4 Å, 5 Å, 6 Å, 7 Å, 8 Å, 9 Å, 10 Å, 1.1 nm, 1.2 nm, 1.5 nm, 2nm, or 5 nm. In embodiments, the overcoat can have thickness of lessthan 5 nm.

It can be advantageous to have an ALD overcoat as described herein toimprove the catalytic nanoparticles stability (e.g., resistance tosintering). It has been found, however, an ALD overcoat can decreasecatalytic nanoparticle activity towards alkenes if it is too thick. Ithas been found that over coat thickness of less than 5 nm can provideimproved stability without reduction of the catalytic activity.

The ALD overcoat can cover approximately about 5% or more of the totalsurface area of the catalytic nanoparticles. In embodiments, the ALDovercoat can cover approximately about 5% to about 80%, or about 10% toabout 70%, or about 10% to about 60%, or about 20% to 60%, or about 30%to 60%. For example, the ALD overcoat can cover approximately about 5%,

In embodiments, the alkane dehydrogenation catalyst can include about0.05 wt % nanoparticles to about 0.6 wt % nanoparticle, based on thetotal weight of the alkane dehydrogenation catalyst. In embodiments, thealkane dehydrogenation catalyst can include about 0.05 wt %, 0.06 wt %,0.07 wt %, 0.08 wt %, 0.09 wt %, 0.1 wt %, 0.2 wt %, 0.3 wt %, 0.4 wt %,0.5 wt %, or 0.6 wt %, based on the total weight of the alkanedehydrogenation catalyst.

In embodiments, the alkane dehydrogenation catalyst can have about 50%to about 90% of active metal nanoparticle sites, as measured by theChemisorption Test Method. In embodiments, the alkane dehydrogenationcatalyst can have about 50% to 90%, about 60% to about 85%, or about 70%to about 85%, or about 55% to about 80%, or about 40% to about 80%, orabout 50% to about 60%, of active metal nanoparticle sites, as measuredby the Chemisorption Test Method. For example, the alkanedehydrogenation catalyst can have about 50%, 55%, 60%, 65%, 70%, 75%,80%, 85%, 90%, or 95%, of active metal nanoparticle sites, as measuredby the Chemisorption Test Method.

In embodiments, the alkane dehydrogenation catalyst has improvedstability, for example, as demonstrated by the presence of about 50% toabout 90% active metal nanoparticle sites after annealing for 1 hour at500° C., as measured by the Chemisorption Test Method. The steamtreatment, described further in the Examples herein, is used to simulatethe long-term effects (weeks/months) on the alkane dehydrogenationcatalyst under commercial reaction conditions. In embodiments, thealkane dehydrogenation catalyst can have at least 50%, at least 60%, atleast 70%, or at least 80% active metal nanoparticle sites afterannealing for 1 hour at 500° C., as measured by the Chemisorption TestMethod

In embodiments, the catalytic nanoparticles include at least one metalselected from group 8 metals.

In embodiments, the alkane dehydrogenation catalyst of the disclosurehaving an ALD overcoat can have a hydrogen chemisorption capacity thatis within 20% of the hydrogen chemisorption capacity of an uncoatedalkane dehydrogenation catalyst. In embodiments, the alkanedehydrogenation catalyst of the disclosure having an ALD overcoat, has ahydrogen chemisorption capacity that is within 10% or within 20% of thehydrogen chemisorption capacity of an uncoated alkane dehydrogenationcatalyst as determined by the Chemisorption Test Method described indetail below. In embodiments, the alkane dehydrogenation catalyst of thedisclosure having an ALD overcoat has a hydrogen chemisorption capacitythat is within 5% of the hydrogen chemisorption capacity of an uncoatedalkane dehydrogenation catalyst.

In embodiments, the ALD coated alkane dehydrogenation catalyst caninclude a catalyst support infiltrated with a plurality of catalyticnanoparticles to form an alkane dehydrogenation catalyst, wherein thecatalytic nanoparticles comprise at least one metal selected from group8 metals, and the catalyst support is an extrudate, and an atomic layerdeposition overcoat comprising Al₂O₃.

In embodiments, the atomic layer deposition overcoat is deposited ontothe alkane dehydrogenation catalyst by 2-5 cycles of atomic layerdeposition when the alkane dehydrogenation catalyst has a surface areaof 80 m²/g to 100 m²/g or 5-8 cycles of atomic layer deposition when thealkane dehydrogenation catalyst has a surface area of 80 m²/g to 100m²/g.

In embodiments, the ALD coated alkane dehydrogenation catalyst caninclude a catalyst support infiltrated with a plurality of catalyticnanoparticles to form an alkane dehydrogenation catalyst, wherein thecatalytic nanoparticles can include at least one metal selected fromgroup 8 metals, and the catalyst support is an alumina extrudate; and anatomic layer deposition overcoat; wherein the alumina extrudate is in aγ phase, a θ phase, a α phase, or a combination thereof.

Methods of Preparing an Alkane Dehydrogenation Catalyst

In accordance with embodiments, a method of manufacturing an alkanedehydrogenation catalyst is provided. The alkane dehydrogenationcatalyst can include a catalyst support, catalytic nanoparticles, and anovercoat, and can have any of the attributes and features as describedabove for any of the embodiments herein. In embodiments, the catalystsupport can be an extrudate.

The method of manufacturing an alkane dehydrogenation catalyst caninclude calcining the catalyst support, immersing the calcined catalystsupport in a nanoparticle solution thereby forming a catalyst precursorimpregnated with the nanoparticle precursor, calcining the impregnatedcatalyst precursor under conditions sufficient to convert thenanoparticle precursor impregnated in the catalyst precursor tocatalytic nanoparticles, depositing by atomic layer deposition (ALD) theovercoat onto the calcined catalyst precursor by contacting the calcinedcatalyst precursor with an ALD precursor and water, and repeating thedepositing step one or more times, thereby forming a catalystintermediate, and annealing the catalyst intermediate in air, therebyforming the alkane dehydrogenation catalyst.

In embodiments, the method can include determining a percentage ofactive catalytic sites by testing the H₂ chemisorption using theChemisorption Test Method after a first ALD deposition of the overcoatbefore repeating the depositing step one or more times. The depositingstep can be repeated if the percent catalytically active sites is atleast about 50% as measured by the Chemisorption Test Method. Thedepositing step can be repeated, with intervening testing of the percentof catalytically active sites between deposition cycles. This can ensurea sufficient number of catalytically active sites remain, whilemaximizing the coating that can be applied. This can also allow themethod of the disclosure to be tailored to different catalytic supportsand catalytically particles, which may react differently in terms of thenumber of active sites remaining after the ALD coating process. Forexample, as show in Example 6, low surface area materials were found toallow for increased number of ALD cycles while maintaining a suitablenumber of active sites for the catalytic purposes. Intermittent testingof the percent active sites using the Chemisorption Test Method canadvantageously allow one to determine the precise number of ALD coatingcycles that result in a desired catalyst, balancing catalytic activityagainst the thickness of the ALD coating and thereby the amount ofstability afforded against sintering. The catalyst can be tested anynumber of times during the coating cycle, for example, after each cycle,after 2 or more cycles, or after any suitable number of cycles. Testingcan be done at different increments of the coating cycles, as well. Forexample, a first testing can be performed after a two or more cycles areperformed and then repeated between each subsequent cycle. Inembodiments, the deposition can be repeated until at least about 90%,80%, 70%, 60%, or 50% of the catalytically active sites remain asmeasured by the Chemisorption Test Method. Any suitable threshold valueof catalytically active sites can be selected depending on the catalystbeing formed and desired applications. The methods of the disclosureadvantageously allow for such tailoring of the ultimate catalyticactivity and stability.

In embodiments, methods of the disclosure can utilize the ChemisorptionTest Method to validate catalytic activity during production, forexample, during commercial production, by selectively testing the coatedcatalysts from batches of the production.

In embodiments, method of the disclosure can utilize the ChemisorptionTest Method in determining a suitable number of ALD coating cycles thatcan be performed while obtaining a desired threshold value of the activesites. In such embodiments, the Chemisorption Test Method can be usedintermittently between coating cycles. In embodiments, the method caninclude performing ALD coating cycles until the threshold value ofactive sites is failed, as measured by the Chemisorption Test Method.This can help to identify the maximum number of coating cycles that canbe performed while meeting the threshold hold active sites. The coatingcycle determination made in such a method can then be used for alarger-scale production of the catalyst. As noted above, even duringsuch larger-scale production, the Chemisorption Test Method can be usedon selected catalysts from batches as a validation that the method isresulting in catalyst with desired active sites and that consistentresults are being achieved.

In embodiments, the catalyst support can be calcined at a temperature ofabout 500° C. to about 1200° C., or about 500° C. to about 1050° C., orabout 600° C. to about 1050° C., or about 500° C. to about 800° C., orabout 600° C. to about 800° C., or about 750° C. to about 1050° C. Inembodiments, the temperature can be about 500° C., 600° C., 750° C.,1050° C., 1100° C., 1150° C., or 1200° C.

In embodiments, the catalyst support can be calcined for about 1 hour ormore. For example, the catalyst support can be calcined for about 2hours, 3 hours, 4 hours, 5 hours, 8 hours, 10 hours, 12 hours, 15 hours,20 hours, or 24 hours.

In embodiments, after calcining the catalyst support, the calcinedcatalyst support can have a total surface area of 50 m²/g to 350 m²/g.In embodiments, after calcining the catalyst support, the calcinedcatalyst support can have a total surface area of 50 m²/g to 350 m²/g, apore volume of 0.8 cm³/g to 0.4 cm³/g, and an average pore size of 3 nmto 20 nm as determined by Hg porosimetry.

Calcining of the catalyst support can advantageously provide changes inthe surface area, pore volume, and pore size of the catalyst support, inturn, this can allow for the alkane dehydrogenation catalyst to betailored for high catalytic activity and selectivity, as well as highresistance to sintering and overall longevity of the alkanedehydrogenation catalyst.

The calcined catalyst support can be immersed in a nanoparticleprecursor solution comprising a nanoparticle precursor. The nanoparticleprecursor solution can include the nanoparticle precursor and water orother suitable solvent. In embodiments, the nanoparticle precursorsolution can include the nanoparticle precursor dissolved in water. Inembodiments, nanoparticle precursor is present in the nanoparticleprecursor solution at a concentration of about 0.01 M to about 6 M, orabout 0.1 M to about 3 M, or about 0.1 M to 1 M, or about 0.5 M to 2.5M, or about 1 M to about 2 M. For example, the nanoparticle precursor ispresent in the nanoparticle precursor solution at a concentration ofabout 0.01 M, 0.1 M, 0.5 M, 1 M, 1.5 M, 2 M, 2.5 M, 3 M, 4 M, 5 M, or 6M.

The nanoparticle precursor as disclosed herein can include one or moregroup 8 transition metals. In embodiments, the nanoparticle precursorcan include one or more of H₂ PtCl₆, chloroplatinic acid, ammoniumchloroplatinate, bromoplatinic acid, platinum trichloride, platinumtetrachloride hydrate, platinum dichlorocarbonyl dichloride,tetraamineplatinum chloride, dinitrodiaminoplatinum, and sodiumtetranitroplatinate (II). In embodiments, the nanoparticle precursor isor includes H₂ PtCl₆.

After immersion in the nanoparticle precursor solution, the impregnatedcatalyst precursor is again calcined, and can be calcined underconditions sufficient to convert the nanoparticle precursor impregnatedin the impregnated catalyst precursor to catalytic nanoparticles to forma calcined catalyst precursor. For example, the calcining of theimpregnated catalyst precursor can be done at a temperature in a rangeof about 500° C. to about 1200° C. In embodiments, the temperature canbe about 500° C. to about 1200° C., or about 500° C. to about 1050° C.,or about 600° C. to about 1050° C., or about 500° C. to about 800° C.,or about 750° C. to about 1050° C. In embodiments, the temperature canbe about 500° C., 600° C., 750° C., 1050° C., or 1200° C. Inembodiments, the impregnated catalyst precursor can be calcined forabout 10 minutes or more. For example, the impregnated catalystprecursor can be calcined for about 10 minutes, 30 minutes, 1 hour, 2hours, 3 hours, 4 hours, 5 hours, 8 hours, 10 hours, 12 hours, 15 hours,20 hours, or 24 hours. In embodiments, the catalyst precursor can becalcined for about 0.5 hours to 3 hours. Suitable times and temperaturescan be selected and tailored based on the nanoparticle precursormaterial.

The ALD overcoat can be deposited through atomic layer deposition ontothe calcined impregnated catalyst precursor using an ALD precursor andwater. Deposition of the ALD overcoat can be done at a temperature in arange of about 125° C. to about 500° C., or about 150° C. to about 300°C., or about 175° C. to about 275° C., or about 175° C. to about 250° C.For example, the deposition of the ALD overcoat can be done at atemperature of 125° C., 150° C., 175° C., 200° C., 225° C., 250° C.,275° C., 300° C., 400° C., or 500° C.

In embodiments, the overcoat can be deposited onto the calcinedimpregnated catalyst precursor under vacuum.

In embodiments, the ALD precursor can include one or more of Al, Ti, Nb,Zr, and V. Reference herein will be made to a “ALD precursor” and shouldbe understood to include embodiments of a single gas as well asembodiments of a mixture of gasses. In embodiments, the ALD precursorcan include one or more of Al(CH₃)₃, TiCl₄, ZrCl₄, Zr(N(CH₃)₂)₄,Nb(OCH₂CH₃)₅, and V(O)(OCH(CH₃)₂)₃. In embodiments, the ALD precursor isTMA.

The depositing step can be repeated one or more times, thereby forming acatalyst intermediate. In embodiments, the depositing step can berepeated 2 to 200 times, or 2 to 100 times, or 2 to 50 times, or 2 to 20times, or 2 to 10 times, or 2 to 8 times, or 3 to 6 times. For example,the depositing step can be repeated 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20,25, 30, 50, 100, or 200 times. In embodiments, the growth rate of theALD overcoat can be about 0.1 nm to 0.14 nm per ALD cycle (depositingstep). It has been found that depositing the ALD overcoat onto thecalcined impregnated catalyst precursor can be advantageous when thedepositing step is repeated 2 to 8 times, or 3 to 6 times, as thecatalytic nanoparticles are then both resistant to sintering andmaintain good catalytically active. The thickness of the ALD overcoat isadvantageous when it is about 0.2 nm to about 1.3 nm, as the catalyticnanoparticles are then both resistant to sintering and catalyticallyactive.

Depositing an atomic layer overcoat by ALD on porous supports, such asthe extrudates disclosed herein, can be more complicated than depositingan ALD overcoat on a traditional planar support. The diffusion of theprecursors and products into and out of the high-aspect-ratio pores canbe slow. Advantageously, the methods disclosed herein can deposit anatomic layer overcoat by ALD on porous supports, such as extrudates,without altering the size of the nanoparticles.

Further, the catalyst intermediate can be annealed. Annealing thecatalyst intermediate can take place in open air at a temperature ofless than about 600° C. for a period of time, thereby forming the alkanedehydrogenation catalyst. In embodiments, the temperature can be lessthan about 550° C., or about 450° C. to 600° C., or about 450° C. to550° C. For example, the catalyst intermediate can be annealed at atemperature of about 500° C. In embodiments, the catalyst intermediatecan be annealed for about 15 minutes to about 6 hours, or about 30minutes to about 3 hours, or about 30 minutes to 2 hours, or about 30minutes to 1.5 hours. For example, the catalyst intermediate can beannealed for about 1 hour.

Method of Converting Alkane to Alkene.

Further provided herein is a method of converting an alkane to an alkeneusing the catalyst of the disclosure. The method of converting an alkaneto an alkene can include flowing a gaseous reactant mixture over thealkane dehydrogenation catalyst. The gaseous reactant mixture caninclude alkane gas and optionally, hydrogen gas, wherein the alkane gasis converted to an alkene as the gaseous reactant mixture is flowed overthe alkane dehydrogenation catalyst. In embodiments, the temperature canbe in a range of about 400° C. to about 800° C.

In embodiments, the gaseous reactant mixture can include an alkane gas.In some embodiments, the alkane gas can include one or more of ethane,propane, butane (e.g., isobutane), pentane, hexane, heptane, octane,nonane, and further higher alkanes. The alkane gases as used herein canbe straight chained or branched alkanes. In embodiments, the alkane gascan be one or more of ethane, propane, and butane (e.g., isobutane). Insome embodiments, the alkane is propane and/or isobutane. Inembodiments, the gaseous reactant mixture can include hydrogen gas. Inembodiments the gaseous reactant mixture can include hydrogen gas, theratio of hydrogen gas to alkane gas can be about 5:1 to about 1:100,based on volume%, or about 2:1 to about 1:10, or about 1:1 to about1:10, or about 1:2 to about 1:10. For examples, the ratio of hydrogengas to alkane gas can be 5:1, 3:1, 2:1, 1:1, 1:2, 1:3, 1:4, 1:5, 1:10,or 1:100.

The alkane gas is converted to an alkene as the gaseous reactant mixtureis flowed over the alkane dehydrogenation catalyst. In embodiments, thealkene can be one or more of ethylene, propylene, butylene (e.g.,isobutylene), pentene, hexene, heptene, octene, nonene, and furtherhigher alkenes. In embodiments, the alkene can be one or more of ethene,propene, and butene. In some embodiments, the alkene is propene and/orisobutylene. In embodiments, the propane gas is converted to propyleneor the isobutane gas is converted to isobutylene, as the gaseousreactant mixture is flowed over the alkane dehydrogenation catalyst.

The gaseous reactant mixture is flowed over the alkane dehydrogenationcatalyst at any suitable space velocity. In embodiments, the spacevelocity can be about 10,000 h⁻¹to about 700,000 h⁻¹, or about 30,000h⁻¹to about 650,000 h⁻¹, or about 50,000 h⁻¹to about 600,000 h⁻¹, orabout 60,000 h⁻¹to about 600,000 h⁻¹, or about 60,000 h⁻¹to about120,000 h⁻¹, or about 300,000 h⁻¹to about 600,000 h⁻¹. In embodiments,the space velocity can be about 60,000 h⁻¹, about 66,000 h⁻¹, about72,000 h⁻¹, about 75,000 h⁻¹, about 78,000 h⁻¹, about 84,000 h⁻¹, about90,000 h⁻¹, about 105,000 h⁻¹, about 120,000 h⁻¹, about 300,000 h⁻¹,about 330,000 h⁻¹, about 360,000 h⁻¹, about 375,000 h⁻¹, about 390,000h⁻¹, about 420,000 h⁻¹, about 450,000 h⁻¹, about 525,000 h⁻¹, or about600,000 h⁻¹. For example, space velocity can be measured as LHSV=volumeflow rate of feed in sccm/catalyst loading in cc. For a 0.5 wt % Ptcatalyst loading and a flow rate of 200 sccm of feed, the catalyst usedfor testing was ˜0.15 g and the estimated catalyst loading in cc is 0.04cm³. So the LHSV is (200 sccm*60)/0.04 cm³=300,000 h⁻¹. For example, a0.1 wt % Pt catalyst and a flow rate of 250 sccm of feed, five timesmore catalyst was tested, so the estimated catalyst loading in cc is 0.2cm³. So the LHSV is (250 sccm*60)/0.2 cm³ =75,000 h⁻¹.

In embodiments, the equilibrium conversion of alkane to alkene can beabout 15% to about 50%, or about 20% to about 45%, or about 25% to about40%, or about 30% to about 40%. In embodiments, the equilibriumconversion of alkane to alkene can be about 30% to about 40%.

In embodiments, the catalyst experiences a total amount of thermalcracking of less than about 3% after about 20 hours. In embodiments, thecatalyst experiences a total amount of thermal cracking of less thanabout 1% after about 20 hours.

The alkane dehydrogenation catalysts of the disclosure can have aselectivity to alkenes of greater than about 70%. In embodiments, thealkane dehydrogenation catalyst can have a selectivity to alkenes ofgreater than about 85%. For example the alkane dehydrogenation catalystcan have a selectivity to alkenes of about 70% to 100%, or about 70% toabout 99.9%, or about 70% to about 99%, or about 70% to about 95%, orabout 85% to 100%, or about 85% to about 99%, or about 85% to about 95%,or about 85% to about 90%, such as, 70%, 75%, 80%, 85%, 90%, 95%, 98%,99%, 99.9%, 100%.

Examples of atomic layer deposition methodologies and conditions whichcan be applicable for the use of the methods of the disclosure, can befound in the following publications, which are incorporated herein byreference, U.S. Pat. Nos. 9,284,643 & 9,546,424.

Chemisorption Test Method

H₂ chemisorption was performed using a Micromeritics ASAP 2020 analyzerusing the double isotherm method (Perrichon et al., Appl Catal a-Gen2004, 260 (1), 1-8). The first isotherm provides the total amount ofchemisorbed hydrogen; the second isotherm gives the reversiblechemisorbed hydrogen. The difference between the two isotherms is theirreversibly chemisorbed hydrogen on the platinum surface.

For example, the H₂ chemisorption can be tested by using a sample (i.e.,alkane dehydrogenation catalyst) that was reduced in H₂ at 773 K andre-oxidized at 313 K. The H₂ chemisorption was performed at 313 K togenerate the first isotherm, which gives the total amount of chemisorbedhydrogen. At the same temperature, the second isotherm was generated,which gives the reversible bound chemisorbed hydrogen, the differencebetween the two isotherms giving the irreversible chemisorbed hydrogen,which corresponds to hydrogen adsorbed on the catalyst surface (e.g.,Pt). The two isothermal curves were drawn in the 70 to 400 mmHg pressuredomain.

EXAMPLES

In the examples below, characterization of the resulting catalysts andmethods of converting alkanes to alkenes were characterized using thefollowing techniques.

Steam Treatment—To simulate long term deactivation, all newly madealkane dehydrogenation catalysts were subjected to steaming at 700° C.The procedure used was as follows: A fraction of the alkanedehydrogenation catalyst was placed in a ceramic boat. The ceramic boatwas placed inside of a horizontal quartz tube located inside of ahorizontal tube furnace. Dry nitrogen was flowed through the reactorwhile the furnace was heated to the steaming temperature. When thedesired temperature was reached, the flow of nitrogen was diverted sothat it flowed through a water bubbler to saturate the gas with water.The N₂/water gas was then flowed over the catalyst for the prescribedtime.

Example 1

Catalyst synthesis. Alumina extrudates were synthesized by peptizingVersal-251, a boehmite alumina produced by UOP with nitric acid andextrusion as 1/16″ cylinders. The dried extrudates were calcined attemperatures ranging from 500° C. to 1185° C. to generate Al₂O₃ baseswith varying surface area and porosity. Pt was impregnated at 0.1wt %and 0.5wt % via standard incipient wetness procedures featuringsolutions of Pt precursor. Prior to Pt impregnation, the Al₂O₃extrudates had been calcined at 500° C. (ultra-high SA), 600° C. (highSA), 750° C. (medium SA), 1050° C. (low SA), or 1185° C. (ultra-low SA)to adjust the surface area. After impregnation, the catalysts,comprising Pt, were oxidized at a temperature of about 500° C. in air,and prior to next steps, then reduced in an atmosphere comprising H₂ ata temperature of about 500° C. For catalysts comprising extrudatespreviously calcined at 1185° C., this oxidation and reduction wasperformed at 250° C. Al₂O₃ ALD was performed on the Pt/Al₂O₃ catalystextrudates in a fixed bed ALD reactor at 200° C. using alternatingexposure to trimethylaluminum (TMA) and deionized water on a PrometheusP6 reactor (available from Forge Nano). TiO₂ ALD was performed on thesame reactor using alternating exposure to titanium tetrachloride(TiCl₄) and deionized water at 150° C. An integrated mass spectrometeron the reactor exhaust monitored the ALD reaction in real time. Prior todeposition, the extrudates were degassed under nitrogen flow at 300° C.to remove adventitious water from the surfaces before lowering thetemperature to the deposition temperature and proceeding with the ALDprocess. The catalysts below are categorized using shorthand shown here:ncAlO/xPt/m, wherein the n represents the number of Al₂O₃ ALD cycles(c), x represents the initial Pt loading (in wt. %), and m representsthe catalyst support Al₂O₃ extrudates name: ultra-high SA=280 m²/g; highSA=256 m²/g; medium SA=211 m²/g; low SA=90 m²/g; ultra-low SA=8 m²/g.

Characterization. N₂ physisorption were measured at 77 K with aMicromeritics ASAP 2020 analyzer to characterize the specific surfacearea and the pore size changes. Prior to the measurement, the sampleswere degassed overnight at 250° C. Thermogravimetric analysis (TAInstruments, Discovery TGA 5500) was used to investigate the moistureloss from the extrudates. In the TGA experiments, around 5 mg of anextrudate were placed in a crucible. The crucible was heated from roomtemperature to 700° C. at the rate of 10° C./min in ultra-high purityargon (99.999% ) at a flow rate of 10 mL/min. Elemental compositions ofthe samples were determined by inductively coupled plasma (ICP) massspectroscopy. Scanning transmission electron microscopy (STEM) imageswere taken at Electron Microscopy Center at Argonne National Laboratoryusing an FEI Talos Scanning Transmission Electron Microscope. The Ptparticle sizes were determined using ImageJ software by counting about100 to 200 particles from the images for each sample. The STEM isequipped with an energy-dispersive spectrometer (EDS). The lamellas forEDS mapping were prepared by using the Zeiss 1540X6 focused ionbeam-scanning electron microscopy (FIB-SEM). H₂ chemisorption wasperformed using a Micromeritics ASAP 2020 analyzer using the doubleisotherm method (Perrichon et al., Appl Catal a-Gen 2004, 260 (1), 1-8).The first isotherm provides the total amount of chemisorbed hydrogen;the second isotherm gives the reversible chemisorbed hydrogen. Thedifference between the two isotherms is the irreversibly chemisorbedhydrogen on the platinum surface. Diffuse Reflectance Infrared FourierTransform Spectroscopy (DRIFTS) was acquired using a Thermo ScientificNicolet iS50 FTIR spectrometer equipped with an iS50 Automated Beamsplitter exchanger (ABX). Catalysts were first reduced at 500° C. for 1h in 2.8% H₂/Ar, then exposed to 30 mL/min 1% CO/He for 10 min andpurged with 30 mL/min He. The spectra were collected after the He flushevery 2 min. After that, sample was exposed to 30 mL/min air for 1 h,purged with He for 20 min and then reduced in 2.8% H₂/Ar for 1 h. Afterreduction, the sample was exposed to 30 mL/min 1% CO/He for 10 min andpurged with 30 mL/min He. The spectra were collected right after the Heflush for every 2 min. X-ray Absorption Spectroscopy (XAS) measurementswere conducted at the Pt L3 edge (˜11 564 eV) at beamline 10-BM of theMaterials Research Collaborative Access Team (MRCAT) at the AdvancedPhoton Source (APS) at Argonne National Laboratory. The XAS spectra wererecorded in the transmission mode. The samples were pressed into acylindrical holder that can hold six samples simultaneously. The loadingof the sample was optimized to achieve a step height of 1. Before themeasurement, the samples were fully reduced in 3.5% H₂ in helium at 523K for 30 min, and subsequently cooled to room temperature in ultra-highpurity helium.

Example 2

Measurement of catalytic activity. The catalytic reaction for propanedehydrogenation at atmospheric pressure was carried out in a verticalquartz tubular reactor with a diameter of 10 mm. The quartz tube reactorwas placed within a furnace. The catalyst was supported on quartz woolwith an internal thermocouple monitoring the temperature of the catalystbed. Approximately 120 mg of 0.5% Pt catalysts and 600 mg of 0.1% Ptcatalysts were crushed to 60-80 mesh and then loaded for testing. Forcatalysts with ALD overcoating, the amount of catalysts added wasadjusted to keep the same Pt content in the reactor based on the Ptloading from ICP analysis. Two grams of quartz sand (80 mesh size) wasused to dilute the catalyst to improve the temperature uniformity.Before the measurement, the catalyst was reduced in 10% H₂ for 0.5 h at500° C. The ALD overcoated catalyst, as prepared in Example 1, wascalcined in air for 1 h before the reduction. The reactant mixtureconsisted of 50/50 vol % of hydrogen (Airgas, 99.999% ) and propane(Airgas, 99.5% ), with a total flow of 260 mL/min. The reaction wascarried out at 600° C. The temperature was monitored by a thermocoupleinserted into the catalyst bed. The concentration of the reactants andproducts was measured by an online gas chromatograph (GC, Agilent 6890)equipped with a flame ionization detector (FID) and a thermalconductivity detector (TCD). The propane conversion, propyleneselectivity, and propylene yield were calculated directly as follows:

${{C_{3}H_{8}{Conversion}} = {\frac{{{moles}{of}C_{3}H_{8in}} - {{moles}{of}C_{3}H_{8out}}}{{moles}{of}C_{3}H_{8in}} \times 100\%}}{{C_{3}H_{6}{Selectivity}} = {\frac{{moles}{of}C_{3}H_{6}}{{{moles}{of}C_{3}H_{6}} + \frac{{moles}{of}C_{2}}{3/2} + \frac{{moles}{of}{CH}_{4}}{3}} \times 100\%}}{{C_{3}H_{6}{Yield}} = {C_{3}H_{8}{Conversion} \times C_{3}H_{6}{selectivity} \times 100\%}}$

Catalyst Performance. FIG. 5 shows the C₃H₈ conversion vs C₃H₆selectivity for 0.1% and 0.5% Pt catalysts prior to ALD modification,which were prepared according to Example 1. The C₃H₈ conversiondecreased from 18% to 10% for all catalysts except for catalyst 0.5Pt/ultra-low SA (which decreased from 10% to 4% ). The low C₃H₈conversion (<10% ) was due to the formation of unevenly distributedlarger Pt nanoparticles (cf. Table 2), since at the same Pt loading,increases in the Pt particle size led to a decrease in the number ofsurface Pt sites. Pt nanoparticle sintering was another possible reasonof low conversion for this ultra-low surface area catalyst, which had ahigher probability of encountering other Pt during the reaction. Thus,ALD overcoating was not applied for catalysts on ultra-low surface areasupport because the C₃H₈ conversion dropped to 4%. The C₃H₆ selectivityfor all catalysts is above 85%.

The average Pt nanoparticles size remained at 0.88±0.11 nm after 20 hunder reaction conditions for a non-ALD overcoated catalyst (0.5Pt/medium SA). Comparatively, the fresh versus steamed catalysts(0.92±0.19 nm, derived from STEM images), had no obvious visible changeof the Pt nanoparticles. Since even 20 hr on stream in the lab reactorcannot simulate long term catalyst deactivation, steam treatment wasused to simulate the long-term effects (weeks/months) under commercialreaction conditions. The average Pt nanoparticles size after 1 h steamtreatment at 700° C. was 1.96±1.18 nm, which showed the growth of Ptnanoparticles after steaming. In addition, the decrease in chemisorbedH₂ amount in FIG. 4 (c-f) also suggested agglomeration of the Ptnanoparticles. Thus, in testing the C₃H₈ conversion change and longevityimprovement after ALD overcoating, two equal amounts of each catalystwere tested without and with steam pretreatment. Since the Pt loadingwould be changed after ALD overcoating, to load the same amount of Ptfor testing, the amount of each catalyst was adjusted based on the Ptloading from ICP measurement. The C₃H₈ conversion and C₃H₆ yield at the10^(th) hour during the reaction are shown in FIG. 6 . The gray barheight represents the C₃H₈ conversion and C₃H₆ yield for each steamedcatalyst, while the hashed bar height represents the drop (absolutevalue) of C₃H₈ conversion and C₃H₆ yield after steaming compared tofresh catalysts, thus, the total bar height (combine gray and hashed barheight) represents the C₃H₈ conversion and C₃H₆ yield for each freshcatalyst (without steam pretreatment). Generalizing, for all freshcatalysts, it was notable that the C₃H₈ conversion and C₃H₆ yield werenot substantially changing as a function of ALD coating thickness, whichsuggested the overcoated Al₂O₃ by ALD does not block the active Ptsites. For some of the ALD overcoated catalysts, the C₃H₈ conversion andC₃H₆ yield were slightly higher than non-overcoated ones, which wasprobably because of the uneven distributed Pt nanoparticles. Contrarily,the C₃H₈ conversion and C₃H₆ yield of the steamed catalysts (gray barheight) increased as a function of ALD thickness. Thus, the change inC₃H₈ conversion and C₃H₆ yield between the fresh and steamed catalysts(hashed bar height) was decreasing as a function of increasing ALDthickness which suggested that the improvement in catalysts longevityafter ALD overcoating.

Using the results from the H₂ chemisorption, the turnover frequency(TOF, s⁻¹) of C₃H₆ after 10 hours on stream was normalized based on theamount of surface exposed Pt atoms after air annealing in FIG. 4 . FIG.7 showed that the C₃H₆ TOF increased with the increase of Al₂O₃ ALDcycles. If we assume all the surface Pt atoms were active sites for C₃H₆formation and the Al₂O₃ material deposited by ALD was inert, the TOFshould remain the same. As shown in FIG. 6 , the C₃H₆ yield was notsubstantially changed as a function of ALD cycles, thus, the increase inTOF after ALD coverage of surface Pt atoms suggested that the Al₂O₃deposited by ALD blocked the less active Pt sites for C₃H₆ formation,while leaving the most active sites still exposed. The low-coordinatedsurface metal atoms (edge or corner) may be the sites for both metalsintering and coke formation. The overcoated Al₂O₃ appeared toselectively cover those low-coordinated sites, which explained theimprovement in longevity as well as the C₃H₆ TOF. As shown in FIG. 8 ,the C₃H₆ selectivity maintained or slightly increased as a function ofALD cycles and accompanied by the decrease in selectivity for two majorbyproducts, CH₄ and C₂H₆. The product selectivities reported herecorresponded to C₃H₈ conversion at ˜12% for fresh catalysts and ˜7% forsteamed catalysts. The selectivities of CH₄ and C₂H₆ for each catalystwere very similar, suggesting that those two byproducts were mainlyproduced through a hydrogenolysis reaction since the molar ratio forthose two byproducts is 1:1 (C₃H₈+H₂→C₂H₆+CH₄). The slight increase inC₃H₆ selectivity was attributed to the inhibition of this hydrogenolysisreaction due to blockage of the low-coordinated surface Pt sites afterAl₂O₃ ALD. For steamed catalysts, the products selectivity suggested theimprovement in C₃H₆ selectivity after Al₂O₃ ALD decoration.

Example 3

Characterization of Al₂O₃ extrudates. In catalyst synthesis, using highsurface area material as a support can help to disperse and stabilize Ptnanoparticles. However, in terms of ALD coating, low substrate surfacearea is favorable since it would take less time and amount of ALDprecursors to saturate the substrate surface. To investigate the effectsof the surface area of the support on the ALD overcoating process, Al₂O₃extrudates were calcined at 500, 600, 750, 1050, or 1185° C. Table 1shows that increasing the support calcination temperature results in adecrease in the surface area as well as the pore volume, falling from˜280 m²/g to ˜8 m²/g as the consecutive phase transitions from γ-Al₂O₃through θ-Al₂O₃ to α-Al₂O₃ are observed by XRD (Wefers et al., AlcoaResearch Laboratories 1987, Alcoa technical paper, no. 19, rev.). Themoisture loss was seen to decrease as calcination temperature increased,which can be attributed to the loss of surface area and thus surfacehydroxyls. Water loss was then used as a proxy for the amount ofAl(CH₃)₃ required during the ALD overcoating step.

TABLE 1 Textural properties of Al₂O₃ extrudates derived from N₂physisorption and XRD results Total External Pore Average T ^(a) SA SAvolume Pore Size XRD Support (° C.) (m²/g) (m²/g) (cm³/g) (nm) phasename ^(b) 500 280 274 0.70 6.8 γ ultra-high SA 600 256 246 0.66 7.1 γhigh SA 750 211 198 0.64 8.3 γ/θ medium SA 1050 90 83 0.51 16.1 θ/α lowSA 1185 8 7 0.03 15.6 α ultra-low SA ^(a) Al₂O₃ extrudates calcinationtemperature ^(b) SA: surface area

Example 4

Characterization of Pt nanoparticles. FIG. 1 shows representative STEMimages of the non-ALD overcoated Pt catalysts, as described in Example 1prior to the ALD coating process, where the Pt nanoparticles were highlydispersed on support Al₂O₃ extrudates. The average Pt nanoparticles sizeare listed in Table 2. Except for catalyst 0c/0.5 Pt/ultra-low SA, whichhad the largest Pt nanoparticle size (1.12±0.36 nm) due to the limitedsurface area on which to disperse Pt. Other 0.1% and 0.5% Pt loadedcatalysts had average nanoparticle sizes around 0.9 nm with narrow sizedistribution. The amount of the H₂ chemisorbed per Pt was similar foreach 0.1% and 0.5% Pt catalyst, moreover, the increase in Pt loading (5times more from 0.1% to 0.5% ) led to around 5 times more H₂ chemisorbed(4.5 to 24.0 μmol/g), again demonstrating the formation of similar-sizedPt nanoparticles. The only exception was for catalyst 0c/0.5%Pt/ultra-low SA with larger and unevenly dispersed Pt nanoparticlesformed, the amount of H₂ chemisorbed was only 15.9 μmol/g. Peakintensity of the Fourier transformed EXAFS spectra were known to reflectthe average nanoparticles size (Lei et al., Top Catal 2011, 54 (5-7),334-348). Peak intensities are similar among those four catalysts (0.1%and 0.5% Pt on both medium and ultra-high SA supports), again indicatingthe average Pt nanoparticles size was similar. For catalysts onultra-low SA support, the higher peak intensity again suggested largerPt nanoparticles formation.

TABLE 2 Summary of Pt nanoparticles size and H₂ chemisorption resultsAverage Amount of diameter H₂ chemisorbed Sample (nm) (μmol/g) 0.1%Pt/ultra-high SA 0.81 ± 0.13  4.5 0.1% Pt/high SA 0.89 ± 0.13  4.5 0.1%Pt/medium SA 0.90 ± 0.12  4.5 0.1% Pt/low SA 0.87 ± 0.11  4.8 0.1%Pt/ultra-low SA 0.92 ± 0.23  4.9 0.5% Pt/ultra-high SA 0.88 ± 0.16 24.30.5% Pt/high SA 0.92 ± 0.13 21.2 0.5% Pt/medium SA 0.92 ± 0.19 24.0 0.5%Pt/low SA 0.90 ± 0.13 28.4 0.5% Pt/ultra-low SA 1.12 ± 0.36 15.9

Example 5

Characterization of the material properties after ALD. Testing was doneto understand precursor penetration into the Al₂O₃ extrudates. Since itwas not feasible to distinguish Al₂O₃ deposited by ALD from Al₂O₃extrudates, TiO2 ALD (TiCl₄ and H₂O as precursor at 150° C.) wasutilized to understand precursor penetration behavior. To demonstratethe precise control of deposition at atomic level for both Al₂O₃ andTiO₂ ALD, ex situ spectroscopic ellipsometry was used to measure thethin film thickness after 50, 100, and 200 cycles of Al₂O₃ and TiO₂ ALDon clean Si (100) wafers. The thickness of Al₂O₃ and TiO₂ increasedlinearly as a function of ALD cycles with the growth rate of 1.2 and 0.4Å per cycle, respectively. The growth rate for both ALD processes wasthe same as values reported in the literature (Ott et al., Thin SolidFilms 1997, 292 (1-2), 135-144; Aarik et al., Appl Surf Sci 2001, 172(1-2), 148-158). FIG. 2 displays the EDS mapping analysis of medium SAAl₂O₃ extrudates after 5 cycles of TiO₂ ALD. The samples were extractedfrom inside of the Al₂O₃ extrudates by removing the Al₂O₃ from thesurface with the help of a micromanipulator using FIB-SEM. The EDS mapsshowed the homogeneous distribution of Ti across the Al₂O₃ extrudatesporosity.

The N₂ physisorption analysis was applied to investigate the surfacearea and porosity change after different cycles of Al₂O₃ ALDovercoating. As the results shown in FIG. 3 , there was negligiblechange in total surface area and pore volume after 0.1% and 0.5% Ptimpregnation, suggesting the formation of sub-nanometer Ptnanoparticles. As expected, the total surface area and pore volumedecreased (only exception for total surface area of catalysts on low SAsupport in FIG. 3(g)) with additional number of cycles of Al₂O₃ ALD,showing the well-controlled layer by layer Al₂O₃ deposition by ALD. Herewe need to point out that for catalysts on high and medium SA supports,the surface area (FIG. 3(c) and (e)) for the 0.5% Pt impregnatedcatalysts were higher than the 0.1% Pt impregnated catalysts since adifferent batch of Al₂O₃ extrudates support was used. For the catalystson ultra-high SA supports, both 0.1% Pt and 0.5% Pt impregnatedcatalysts were based on the same batch of Al₂O₃ extrudate supports. Acomparison between the 0.1% Pt and 0.5% Pt catalysts showed that thesurface area (FIG. 3(a)) and pore volume (FIG. 3(b)) after the samenumber of ALD cycles were very close demonstrating the excellentrepeatability for the ALD overcoating process. For catalysts on low SAsupport, there was no surface area change after Al₂O₃ ALD overcoating(FIG. 3(g)). Based on the growth rate of 1.2 Å per cycle, the thickestAl₂O₃ layer deposited after 7 cycles of ALD is ˜0.9 nm, which was notthick enough to change the surface area of the support with the largestaverage pore size ˜16.1 nm (cf. Table 1). During the Al₂O₃ ALD process,the precursors TMA and H₂O were sequentially dosed into the ALD chamberat 200° C. under vacuum. To exclude the possibility of Pt nanoparticlessize change after ALD, STEM images were taken on catalyst 10cAlO/0.5Pt/low SA, which was the highest possibility for Pt nanoparticlessintering. Since this catalyst had the longest time in the ALD reactorafter 10 cycles of Al₂O₃ ALD and due to the lowest surface area (Ptcatalysts on ultra-low SA supports will not be studied, cf. FIG. 5 ), Ptnanoparticles had the least space to get separated. The Pt particle sizeremained the same (0.83±0.11 nm) suggesting that the ALD overcoatingdoes not change the particle size. Thus, it was concluded that the ALDprocess does not alter the Pt nanoparticles size.

Example 6

Catalysts testing condition. In general, dehydrogenation of propane is ahighly endothermic reaction requiring heating to 500 to 700° C. Asreported previously, due to the positive effect of decreasing cokeprecursor coverage, the reaction rate was accelerated by co-feedingpropane with hydrogen, thus, the equilibrium conversion was calculatedby HSC Chemistry based on different C₃H₈ to H₂ ratio (H.S.C. Software,Outokumpu HSC chemistry for windows, Version 5.1, AnttiRoine,02103-ORC-T, Pori, Finland, 2002; Saerens et al., Acs Catal 2017, 7(11), 7495-750). The catalyst tested herein were synthesized asdescribed in Example 1. The equilibrium conversion decreased withincreasing H₂ concentration. In the disclosure herein, the reactiontemperature was set to 600° C. To minimize the coke formation inevaluation of catalyst stability due to Pt nanoparticle sintering,hydrogen was co-fed with propane with C₃H₈:H₂ molar ratio set to 1:1.Under this condition the equilibrium conversion is 36%. The C₃H₈conversion from thermal cracking decreased with the increase of thetotal flow rate. To minimize the effect of high thermal crackingconversion in the analysis of the catalytic performance, total flow ratewas set to 260 sccm. Here the thermal cracking conversion was below 1%.

Upon annealing in flowing air at 500° C. for 1 h, nanopores were createdin an ALD overcoated layer (Karwal et al., J Vac Sci Technol A 2018, 36(1)). Following this high temperature annealing the active surface ofthe underlying Pt nanoparticles can be exposed allowing propanedehydrogenation to occur. IR spectra of CO chemisorption showed thebroad CO band formed at a frequency of 2040-2090 cm⁻¹ and was assignedto linear-bonded CO on Pt. The weaker peaks at 1830 cm⁻¹ were assignedto bridge-bonded CO on Pt. For the catalyst 0.5 Pt/medium SA, after 5,7, and 10 cycles of Al₂O₃ ALD, the intensity of the CO chemisorptionpeaks decreased showing that the exposed Pt atoms are being covered bythe AlOx ALD. After calcination in air at 500° C. for 1 h, the CO peaksbecame more pronounced indicating blockage of the Pt atoms after ALDovercoating and restoration of the gas accessibility to Pt atoms aftercalcination.

H₂ chemisorption was used to further quantify the accessibility of thePt atoms under the overcoated Al₂O₃ layer. As shown in FIG. 4(a) and(b), the amount of adsorbed H₂ decreases with increasing number of ALDcycles for both series of 0.1% and 0.5% Pt catalysts, showing that thePt nanoparticles were gradually coated with Al₂O₃ and the amount ofdeposited Al₂O₃ can be well controlled by the ALD process. FIG. 4 (c-f)shows the chemisorbed H₂ amount for all the 0.5% Pt catalystsinvestigated after air annealing and steaming. After annealing at 500°C. in flowing air for 1 h, more Pt atoms were exposed, which wasattributed to nanopore formation from the overcoated Al₂O₃ layer. Thepercentages of exposed Pt surface sites after ALD overcoating and afterair annealing are listed in Table 3.

The stability for the 0.5% Pt catalysts after ALD overcoating weretested following steam treatment (1 h and 4 h at 700° C.). As can beseen in FIG. 4 (c-f), the lines with diamond and square symbols show theamount of chemisorbed H₂ after steaming for 1 h and 4 h, respectively.The reduction in Pt sites caused by steaming was inversely proportionalto the number of Al₂O₃ ALD cycles. The number of surface Pt sitesfurther decreased after 4 h steaming for non-ALD overcoated catalysts,while the number of Pt sites for the ALD overcoated catalysts werestabilized after 1 h steaming (diamond shaped symbols). The resultsshowed that the use of Al₂O₃ ALD overcoating can improve the catalystsstability to preserve the surface Pt sites.

TABLE 3 The percentage of exposed Pt Surface sites after ALD overcoatingand after air annealing The % of exposed Pt surface sites 2 3 4 5 7 10Catalysts cycles cycles cycles cycles cycles cycles 0.5% After Al₂O₃ ALD— 43 — 22 18 — Pt/ultra- high SA After air annealing — 58 — 40 27 — 0.5%Pt/ After Al₂O₃ ALD 82 55 — 29 27 — high SA After air annealing 90 69 —45 38 — 0.5% Pt/ After Al₂O₃ ALD 72 61 49 42 26 24 medium After airannealing 83 74 63 60 38 34 SA 0.5% After Al₂O₃ ALD 76 67 — 58 22 —Pt/low After air annealing — — SA

Example 7

ALD Coating Process of the Catalyst: FIG. 9 shows images of a 4-cyclepilot-scale and 1-cycle light commercial scale ALD reactors. The ALDused was a sequential vapor-phase deposition technique. The scalingapproach was to spatially segregate ‘A’ and ‘B’ precursor exposures(shown in the embedded schematic in FIG. 9 ) into consecutive chambers.This feature allowed the incorporation of residence time into theprocess sequence, which provided a substantial benefit to catalystsubstrates with accessible porosity that can be coated with sufficientdwell times. Furthermore, ALD is typically operated under vacuumconditions in batch reactors, however the system used herein operated atany nominal operating pressure between rough vacuum, to higher thanatmospheric pressure with minimal process impacts. This system waswell-suited for either powdered catalyst materials, as well as moreconventional commercial extrudates, granules or pelletized materials,and was operated with nearly 100% precursor efficiency whileaccommodating the substantially greater surface areas inherent toheterogeneous catalysts. The flow of powders and gases wereindependently controlled, and powder residence time can be modulated tobalance coating efficiency and production throughput.

Residence time is a key feature of this semi-continuous productionsystem, which provided an invaluable patent-protected process parameter.ALD was already uniquely suited for diffusion and infiltration ofprecursor materials into porous materials and often well outperformedsolution based methods for generating similar materials. However,diffusion of the precursors and byproducts into and out of the highsurface area base material was still the largest challenge. The systemherein provided an ability to control residence time, which is criticalto overcome the diffusion limitations encountered in such substantiallyhigh surface area powders. This also allow for quantitative control ofprecursor delivery and operating pressures, which maximized precursorutilization. Together the residence time, controlled delivery andpressure were used to uniquely tailor the degree of penetration of thecoatings into the interior surfaces of the catalysts. The specificsurface area of any powder was quantifiable using standardinstrumentation techniques, and the elemental content of the metaldeposited in an ALD film was measured using the Inductively CoupledPlasma Optical Emission Spectroscopy (ICP-OES), accurate to the partsper million range. Once a process was developed for the target filmthickness that optimized the functional benefit of the coating, LabViewsoftware was used to execute the appropriate number of ALD “cycles”using fully-controlled exposure times. A highly-robust QA/QC plan wasestablished simply by regularly measuring the surface area of the coatedmaterial, administering a known quantity of moles of each precursor gasinto the reactor, quantifying the amount of reaction byproduct gasleaving the reactor, and measuring the ICP-OES elemental content of theamount of film material deposited on the particle surfaces.

Spatial ALD for powders was chosen because it was ideal for high volume,low ALD cycle systems, and it was envisaged here that less than ˜10 ALDcycles will be required to fully stabilize the catalyst system forbest-in-class durability. Each chamber carried out one ALD“half-reaction”, and in the light-commercial scale system, each stackconstituted one full cycle with an upper holding chamber. Powderedmaterial (or granulates and extrudates for this application) is conveyedfrom chamber to chamber and stack to stack during the semi-continuousprocess. Thus every other chamber in the train is executed the identicalprocess step, and all purging occurred during each conveying step (seeFIG. 9 ). This was the embodiment of “Lean Manufacturing”, as everycomponent in the system was operating at identical throughput and therewas no risk of forming bottlenecks on a production line. Additionally,the production rate was modular and easily controlled, as aloss-in-weight feeder conveyed a desired amount of material into thestarting chamber, and programmable software that individually regulatedthe exact amount of precursor delivered to each chamber can be dialed upor down based on the current production rate; alternatively, pressuresand residence times were used to vary production rates. These featuresenabled the installed capital cost to be minimized.

Alumina extrudates were loaded into an ALD reactor and heated to 300° C.under vacuum to remove adventitious moisture from the system. After twohours, the reactor was cooled to 200° C. for the ALD process. Nitrogenwas flowed through the reactor for the duration of the experiment to actas a carrier gas for the reaction. Trimethylaluminum and water were usedas precursors to form an aluminum oxide ALD overcoat, with methaneforming as the reaction by-product. Different numbers of TMA and water“cycles”, the process of dosing each precursor once to form a monolayerfilm, were completed to form aluminum oxide layers of varying thicknesson the catalyst impregnated alumina extrudates. The reactor was thencooled to room temperature and unloaded. ALD coated extrudates werestored in dry boxes to limit moisture uptake during storage.

The use of the “a” or “an” are employed to describe elements andcomponents of the embodiments herein. This is done merely forconvenience and to give a general sense of the description. Thisdescription should be read to include one or at least one and thesingular also includes the plural unless it is obvious that it is meantotherwise.

Still further, the figures depict embodiments for purposes ofillustration only. One of ordinary skill in the art will readilyrecognize from the following discussion that alternative embodiments ofthe structures and methods illustrated herein may be employed withoutdeparting from the principles described herein.

Thus, while particular embodiments and applications have beenillustrated and described, it is to be understood that the disclosedembodiments are not limited to the precise construction and componentsdisclosed herein. Various modifications, changes and variations, whichwill be apparent to those skilled in the art, may be made in thearrangement, operation and details of the method and apparatus disclosedherein without departing from the spirit and scope defined in theappended claims.

What is claimed:
 1. A method of manufacturing an alkane dehydrogenationcatalyst comprising a catalyst support, catalytic nanoparticles, and anovercoat, the method comprising: calcining the catalyst support at atemperature in a range of about 500° C. to about 1200° C., wherein aftercalcining, the calcined catalyst support has a total surface area of 50m²/g to 350 m²/g; and immersing the calcined catalyst support in ananoparticle precursor solution comprising a nanoparticle precursor,under conditions sufficient to impregnate the calcined catalyst supportwith the nanoparticle precursor and form an impregnated catalystprecursor; calcining the impregnated catalyst precursor under conditionssufficient to convert the nanoparticle precursor impregnated in theimpregnated catalyst precursor to catalytic nanoparticles to form acalcined impregnated catalyst precursor, wherein the calcining is doneat a temperature in a range of about 150° C. to about 600° C.;depositing by atomic layer deposition (ALD) the overcoat onto thecalcined catalyst precursor by contacting the calcined catalystprecursor with an ALD precursor and water at a temperature in a range ofabout 150° C. to about 300° C., and repeating the depositing step one ormore times, thereby forming a catalyst intermediate; annealing thecatalyst intermediate in air at a temperature of less than about 600° C.for about 30 minutes to about 2 hours, thereby forming the alkanedehydrogenation catalyst.
 2. The method of claim 1, further comprisingdetermining a percentage of active catalytic sites using theChemisorption Test Method after depositing the overcoat and beforerepeating the depositing step one or more times.
 3. The method of claim1 or 2, further comprising determining the percentage of activecatalytic sites using the Chemisorption Test Method after repeating thedepositing step at least one time and further repeating the depositingstep if the percentage of active catalytic sites is greater than orequal to 50%.
 4. The method of any one of claims 1 to 3, wherein thecatalyst support comprises Al₂O₃.
 5. The method of any one of claims 1to 4, wherein the catalyst support is an extrudate.
 6. The method of anyone of claims 1-5, wherein the catalyst support is calcined at atemperature in the range of about 500° C. to about 1050° C.
 7. Themethod of any one of claims 1-6, wherein the catalyst support iscalcined at a temperature in the range of about 600° C. to about 800° C.8. The method of any one of claims 1-7, wherein the catalyst support hasa pore volume of 0.8 cm³/g to 0.4 cm³/g, and an average pore size of 3nm to 20 nm as determined by Hg porosimetry.
 9. The method of any one ofclaims 1-8, wherein the catalyst support has an average pore size ofabout 6 nm to about 10 nm as determined by Hg porosimetry.
 10. Themethod of any one of claims 1-9, wherein the nanoparticle precursorsolution comprises the nanoparticle precursor dissolved in water. 11.The method of claim 1, wherein the nanoparticle precursor comprisesgroup 8 transition metals.
 12. The method of claim 11, wherein thenanoparticle precursor comprises one or more of H₂ PtCl₆, chloroplatinicacid, ammonium chloroplatinate, bromoplatinic acid, platinumtrichloride, platinum tetrachloride hydrate, platinum dichlorocarbonyldichloride, tetraamineplatinum chloride, dinitrodiaminoplatinum, andsodium tetranitroplatinate (II).
 13. The method of any one of claims1-12, wherein the nanoparticle precursor is present in the nanoparticleprecursor solution at a concentration of about 0.1 M to about 3 M. 14.The method of any one of claims 1-13, the nanoparticle precursor ispresent in the nanoparticle precursor solution at a concentration ofabout 0.1 M to about 1 M.
 15. The method of any one of claims 1-14,wherein the nanoparticle precursor solution comprises water.
 16. Themethod of any one of claims 1-15, wherein the calcined catalyst supporthas a total surface area of about 70 m²/g to about 300 m²/g.
 17. Themethod of any one of claims 1-16, wherein the ALD precursor comprisesone or more of Al, Ti, Nb, Zr, and V.
 18. The method of claim 17,wherein the ALD precursor comprises one or more of Al(CH₃)₃, TiCl₄,ZrCl₄, Zr(N(CH₃)₂)₄, Nb(OCH₂CH₃)₅, and V(O)(OCH(CH₃)₂)₃.
 19. The methodof any one of claims 1-18, wherein the depositing step is repeated 2 to8 times.
 20. The method of claim 19, wherein the depositing step isrepeated 3 to 6 times.
 21. The method of any one of claims 1-20, whereindepositing the overcoat onto the calcined catalyst precursor occurs at atemperature of about 200° C.
 22. The method of any one of claims 1-21,wherein the overcoat is deposited onto the calcined catalyst precursorunder vacuum.
 23. The method of any one of claims 1-22, wherein the ALDovercoat covers approximately 10% to 60% of the total surface area ofthe catalytic nanoparticles.
 24. An alkane dehydrogenation catalyst,comprising: a catalyst support infiltrated with a plurality of catalyticnanoparticles, and; an atomic layer deposition overcoat; wherein theplurality of catalytic nanoparticles have an average size of about 0.6nm to about 1.2 nm, the atomic layer deposition overcoat has a thicknessof about 1.2 Å to about 1.2 nm, the catalyst support has a total surfacearea of 90 m²/g to 300 m²/g, a pore volume of 0.8 cm³/g to 0.4 cm³/g,and an average pore size of 6 nm to 17 nm.
 25. The alkanedehydrogenation catalyst of claim 24, wherein the catalyst supportcomprises Al₂O₃.
 26. The alkane dehydrogenation catalyst of claim 24 or25, wherein the catalytic nanoparticles comprise platinum.
 27. Thealkane dehydrogenation catalyst of claim 26, wherein the platinumnanoparticles have an average size of about 0.7 nm to about 1 nm. 28.The alkane dehydrogenation catalyst of any one of claims 24-27, whereinthe atomic layer deposition overcoat thickness is about 1.2 Å to about0.8 nm.
 29. The alkane dehydrogenation catalyst of any one of claims24-28, wherein the atomic layer deposition overcoat comprises one ormore of Al, Ti, Nb, Zr, and V.
 30. The alkane dehydrogenation catalystof claim 29, wherein the atomic layer deposition overcoat comprises oneor more of Al₂O₃, TiO₂, ZrO₂, Nb₂O₅, and V₂O₅.
 31. The alkanedehydrogenation catalyst of any one of claims 24-30, wherein the ALDovercoat covers approximately 10% to 60% of the total surface area ofthe catalytic nanoparticles.
 32. The alkane dehydrogenation catalyst ofany one of claims 24-31, wherein alkane dehydrogenation catalystcomprises about 50% to about 90% of active metal nanoparticle sites, asmeasured by the Chemisorption Test Method.
 33. The alkanedehydrogenation catalyst of claim 32, wherein the alkane dehydrogenationcatalyst comprises about 50% to about 90% of active metal nanoparticlesites after annealing for 1 hour at 500° C., as measured by theChemisorption Test Method.
 34. A method of converting an alkane to analkene, comprising: flowing the gaseous reactant mixture over the alkanedehydrogenation catalyst, according to any one of claims 24-33, at atemperature in a range of about 400° C. to about 800° C. wherein thegaseous reactant mixture comprises hydrogen gas and an alkane gas, andthe alkane gas is converted to an alkene as the gaseous reactant mixtureis flowed over the alkane dehydrogenation catalyst.
 35. The method ofclaim 34, wherein the gaseous reactant mixture comprises a ratio ofhydrogen gas to alkane gas of about 2:1 to about 1:10, based on volume%.
 36. The method of claim 34 or 35, wherein a gas hourly space velocityof the method is in a range of about 60,000 h⁻¹to about 600,000 h⁻¹. 37.The method of any one of claims 34-36, wherein the method has anequilibrium conversion of alkane to alkene between about 15% and about50%.
 38. The method of claim 37, wherein the method has an equilibriumconversion of alkane to alkene between about 30% and about 40%.
 39. Themethod of any one of claims 34-38, wherein the catalyst experiences atotal amount of thermal cracking of less than about 3% after about 20hours.
 40. The method of any one of claims 34-39, wherein the catalystexperiences a total amount of thermal cracking of less than about 1%after about 20 hours.
 41. The method of any one of claims 34-40, whereinthe ALD overcoat covers approximately 10% to 60% of the total surfacearea of all the catalytic nanoparticles.
 42. The method of any one ofclaims 34-41, wherein the alkane gas comprises propane gas and/orisobutane gas.
 43. The method of claim 42, wherein the propane gas isconverted to propylene or the isobutane gas is converted to isobutylene,as the gaseous reactant mixture is flowed over the alkanedehydrogenation catalyst.
 44. The method of any one of claims 34-43,wherein the alkane dehydrogenation catalyst has a selectivity to alkenesof greater than about 70%.
 45. The method of claim 44, wherein thealkane dehydrogenation catalyst has a selectivity to alkenes of greaterthan about 85%.
 46. An ALD coated alkane dehydrogenation catalyst,comprising: a catalyst support infiltrated with a plurality of catalyticnanoparticles to form an alkane dehydrogenation catalyst, wherein thecatalytic nanoparticles comprise at least one metal selected from group8 metals, and the catalyst support is an extrudate, and an atomic layerdeposition overcoat arranged in contact with a portion of a surface ofthe catalytic nanoparticles to form the ALD coated alkanedehydrogenation catalyst, wherein the alkane dehydrogenation catalysishas a hydrogen chemisorption capacity that is substantially the same asa hydrogen chemisorption capacity of the ALD coated alkanedehydrogenation catalyst.
 47. An ALD coated alkane dehydrogenationcatalyst, comprising: a catalyst support infiltrated with a plurality ofcatalytic nanoparticles to form an alkane dehydrogenation catalyst,wherein the catalytic nanoparticles comprise at least one metal selectedfrom group 8 metals, and the catalyst support is an extrudate; and anatomic layer deposition overcoat, wherein the atomic layer depositionovercoat is deposited onto the alkane dehydrogenation catalyst by 2-5cycles of atomic layer deposition when the alkane dehydrogenationcatalyst has a surface area of about 80 m²/g to about 100 m²/g or 5-8cycles of atomic layer deposition when the alkane dehydrogenationcatalyst has a surface area of about 80 m²/g to about 100 m²/g.
 48. AnALD coated alkane dehydrogenation catalyst, comprising: a catalystsupport infiltrated with a plurality of catalytic nanoparticles to forman alkane dehydrogenation catalyst, wherein the catalytic nanoparticlescomprise at least one metal selected from group 8 metals, and thecatalyst support is an alumina extrudate; and an atomic layer depositionovercoat; wherein the alumina extrudate is in a γ phase, a θ phase, a αphase, or a combination thereof.